1. Field of the Invention
The present invention relates to wood preservation processes. In particular, the present invention relates to processes for preserving wood by applying mechanical force in the form of vibration, compression, or vibration and compression to kiln-dried or air-dried wood prior to treating the wood with a preservative.
2. Discussion of the Background
The preservation of wood has long been a concern. Various methods of preserving wood have been developed in which wood is treated with a chemical preservative. However, the apparent non-treatability of heartwood faces on southern yellow pine (Pinus spp.) stock has caused much concern in the treating industry. Recently, even greater concern has been generated by the occurrence of what appears to be non-treatable inner sapwood. This inner sapwood does not respond to conventional heartwood indicators and has been referred to as "transition wood". The presence of heartwood and transition wood poses a serious problem when lumber is treated with water-borne preservative, because the heartwood and transition wood remains virtually untreated.
Cech, For. Prod. J., 21(2):41-50, (1970); Cech, Plaff and Huffman, For. Prod. J., 24(7):26-32, (1974); and Gunzerodt, For. Prod. J., 38(2):16-18, (1988) discuss studies using white spruce, Douglas fir, Sitka spruce and yellow birch where transverse compression stresses were applied prior to wood treatment to improve drying and/or treatability. These studies indicated that treatability could be improved by mechanically stressing lumber prior to treatment. In particular, Cech, Plaff and Huffman, For. Prod. J., 24(7):26-32, (1974) used compression forces on spruce heartwood to obtain an increase of 45% in preservative retention. When the same compression forces were combined with increased drying, an increase in retention of 210% was recorded.
Cech and Huffman, For. Prod. J., 20(3):47-52, (1970) reported on a study in which freshly cut, 8/4 samples of eastern white spruce were subjected to varying compression forces prior to treatment with a water-borne preservative. It was determined that deformation or compression amounts of 5% or higher produced an increase in retention and cross-sectional penetration of a preservative.
Cech and Goulet, For. Prod. J., 18(5):90-91, (1968) studied the use of compression to reduce drying time and drying defects. A slight reduction in modulus of rupture occurred in some samples at higher levels of compression or deformation. An increase in preservative retention of 19% was obtained at some of the lower levels of compression with no reduction in modulus of rupture.
However, the above-mentioned articles do not discuss the use of vibration alone or combined with compression to mechanically stress kiln-dried or air-dried wood prior to treatment with a preservative.
U.S. Pat. No. 5,697,414 discloses that combinations of vibration and compression can be used to prevent enzyme-induced sapwood discolorations in freshly-cut hardwood lumber. However, this patent does not discuss the use of vibration and/or compression to increase wood treatability.
Many markets for treated wood are now closed to southern yellow pine with heartwood faces and other refractory wood species because of inadequate preservative penetration in these woods. Thus, there is a need for improved processes for treating and preserving these woods.